1. Field of the Invention
The present invention relates to a package module having a module case in which a circuit board is accommodated.
2. Description of the Related Art
There are various prior art package modules having cases in which circuit boards are accommodated. One such package module is an optical communication module used for optical communications. FIG. 10 is a schematic exploded view of an optical communication module (package module) developed by the applicant of the invention described in the present application. A package module 1 includes a circuit board 2, an optical module unit 3, a module case 4 accommodating the circuit board 2 and the optical module unit 3, and an adapter 5.
The optical module unit 3 includes a circuit portion 3A and a ferrule portion 3B. The circuit portion 3A includes at least one (not shown) of a light-emitting device (e.g., laser diode (LD)) and a photoreceptor device (e.g., photodiode (PD)). In the case of the circuit portion 3A, one or both of a conversion part for converting an electric signal to an optical signal by using the light-emitting device and a conversion part for converting an optical signal to an electric signal by using the photoreceptor device is arranged.
The ferrule portion 3B includes a ferrule (not shown) through which an optical fiber (not shown) passes, a sleeve holding the ferrule, and a ferrule case accommodating the sleeve. The ferrule case is integrated with the case of the circuit portion 3A. One end of the optical fiber passing through the ferrule is exposed at an end surface of the ferrule adjacent to the circuit portion 3A, and the optical fiber is optically coupled to the light-emitting device or the photoreceptor device of the circuit portion 3A. The other end of the optical fiber is exposed at the other external end surface of the ferrule in order to establish external connection.
A unit 7 and a circuit pattern (not shown) are formed on the circuit board 2 to form a circuit. The circuit is electrically connected to a circuit of the optical module unit 3. Such a circuit of the circuit board 2 is, for example, an amplifier circuit for electric signals. In FIG. 10, terminals 8 for connecting the circuit of the circuit board 2 to an external circuit are mounted on the circuit board 2.
The module case 4 includes a base case 9 and a lid case 10. In an inner space defined by an assembly of the base case 9 and the lid case 10, the circuit board 2 and the optical module unit 3 are accommodated. The base case 9 has holes 20 formed through the bottom wall at locations corresponding to the terminals 8 of the circuit board 2. When the circuit board 2 is accommodated in the module case 4, the terminals 8 of the circuit board 2 protrude from the inside of the module case 4 to the outside through the holes 20.
On the periphery of the base case 9 of the module case 4, arms 12 (12A and 12B) are mounted. The arms 12A and 12B are separately arranged to extend out parallel to each other in a lateral direction. The arms 12A and 12B have fixing members 13 (13A and 13B) at their tips, respectively. The arms 12 and the fixing members 13 are used for fitting into an external connector (optical connector) inserted into the adapter 5, described below, to fix the external connector to the package module 1. The arms 12 and fixing members 13 can be integrally formed with the base case 9 by molding.
The adapter 5 includes an adapter case 11 to which the external connector is to be inserted. The adapter case 11 accommodates the arms 12 and fixing members 13 and is attached to the base case 9. The adapter case 11 has an entry 11a to receive an external optical connector at its rear end. As shown in FIG. 11, the adapter case 11 has an opening 11b that is open from the bottom surface to the front end surface. The opening 11b of the adapter case 11 is used for guiding the arms 12 and fixing members 13 into the inner space of the adapter case 11 when the adapter case 11 is attached to the base case 9. The adapter case 11 has fit-receiving portions 15 (15A and 15B) at the front end on the upper wall such that fit-receiving openings 16 (16A and 16B) face down.
The base case 9 has fit projections 17 (17A and 17B) projecting upward at the periphery near the arms 12 (12A and 12B). The fit projections 17 fit into the fit-receiving portions 15 of the adapter case 11. For example, the adapter case 11 is placed above the arms 12 in a position as shown in FIG. 11, and the adapter case 11 is then moved downward toward the arms 12. Therefore, the arms 12 and fixing members 13 are accommodated in the inner space of the adapter case 11 through the opening 11b of the adapter case 11, and the fit projections 17 (17A and 17B) of the base case 9 are fit into the fit-receiving portions 15 (15A and 15B) of the adapter case 11. In this way, the adapter case 11 is attached to the base case 9.
An external optical connector is inserted into the adapter case 11 attached to the base case 9 through the entry 11a, and the external optical connector is then fixed to the base case 9 (package module 1) by using the arms 12 and fixing members 13. Thereby, an end surface of an optical fiber passing through the optical connector and an end surface of an optical fiber passing through the ferrule of the optical module unit 3 are butt-joined.
In the instance shown in FIG. 10, the arms 12 are integrated with the base case 9. However, as shown in FIG. 12, the arms 12 and the fixing members 13 may be formed separately from the base case 9. In such an arrangement, for example, the arms 12 and fixing members 13 are assembled with the adapter case 11, which is formed independently, and the assembly is mounted to the base case 9 with an adhesive or the like. As shown in FIG. 13, aside from the base case 9, an integrated structure of the arms 12, fixing members 13, and the adapter case 11 may be formed by molding. In such an arrangement, the integrated structure is mounted to the base case 9 with an adhesive or the like.
In the instance shown in FIG. 12, however, a manufacturing process is complicated because the process involves the steps of forming the arms 12 and fixing members 13, forming the adapter case 11 independently thereof, assembling the arms 12 and fixing members 13 and the adapter case 11, and then joining the assembly to the base case 9 with an adhesive. Additionally, there are problems in that the reliability of strength of the package module 1 is reduced because adhesive joints lead to low bonding strength and adhesives are prone to deteriorate with age.
In FIG. 13, the adapter case 11, the arms 12, and the fixing members 13 are integrated together. Therefore, the step of assembling the adapter case 11 and both the arms 12 and the fixing members 13 is eliminated. However, for technical reasons in molding, perforations 21 shown in FIG. 13 are opened near the bases of the arms 12. The perforations 21 reduce the strength of the bases of the arms 12, thus increasing the risk of breakage of the arms 12.
In FIG. 10, the base case 9, the arms 12, and the fixing members 13 are integrated together. Therefore, it is not necessary to bond the arms 12 and the base case 9. Also, the perforations 21 resulting from molding are not formed near the bases of the arms 12. However, the adapter case 11 has the wide opening 11b at its bottom surface, and therefore, dust is apt to enter the inside of the adapter case 11 from the opening 11b. As a result, because dust is apt to enter the inside of the adapter case 11 from the opening 11b (for example, when an optical connector is inserted into the adapter case 11 in order to optically couple an optical fiber of the optical connector to an optical fiber of the optical module unit 3) the optical coupling conditions can be degraded by dust entering the adapter case 11.